Use of silver-copper-palladium brazing alloys

ABSTRACT

A compound arrangement comprising a first component of metal being brazed to a second component of metal. The first component has an external cylindrical surface touching an cylindrical internal surface of the second component. The second component clasps the first component tightly, so that the second component exerts compressive stress on said external surface of the first component.

FIELD of the INVENTION

This invention deals with a novel use of silver-copper-palladium brazingalloys.

BACKGROUND of the INVENTION

Such brazing alloys are commercially available, cf. “Welding Journal,October 1990, pages 31 to 34, which describes, among many other brazingalloys whose ability to wet 316L steel is investigated, a 68Ag-27Cu-5Pdbrazing alloy designated as “Palcusil 5”, a 58Ag-32Cu-10Pd brazing alloydesignated as “Palcusil 10”, a 65Ag-20Cu-15Pd brazing alloy designatedas “Palcusil 15”, and a 54Ag-21Cu-25Pd brazing alloy designated as“Palcusil 25”.

Since these silver-copper-palladium brazing alloys properly wetstainless steel, they can be used for brazing components made of thismaterial. It is also possible, however, to braze components of titaniumwith these silver-copper-palladium brazing alloys.

SUMMARY OF THE INVENTION

When examining how to braze a component of titanium to a component ofstainless steel, i.e. without first having to apply an intermediatelayer of another metal to the steel, for instance nickel to 304L steel,cf. “Welding Journal, May 1991, page 112, the inventor first noted onlythat, if flat surfaces of the two components are brazed, the joint isbrittle after having cooled down.

This is due to the rather different coefficients of thermal expansion ofthese two materials; the expansion coefficient of steel is quite a bitgreater than that of titanium.

Surprisingly, however, silver-copper-palladium brazing alloys, whichhave hitherto been offered only for the brazing of components of thesame material, are also very well suited for brazing titanium tostainless steel if, according to one feature of the invention, thesecond component, i.e., the component of stainless steel, clasps thefirst component, i.e., the component of titanium, tightly, so that thecold joint is under constant compressive stress.

Accordingly, a first variant of the invention consists in the use ofsilver-copper-palladium brazing alloys for brazing a first component oftitanium to a second component of stainless steel which clasps the firstcomponent tightly.

A second variant of the invention provides a method for forming acompound arrangement by brazing a first component of titanium to asecond component of stainless steel which clasps the first componenttightly, using silver-copper-palladium brazing alloys, wherein

-   -   the first component of titanium is provided with a cylindrical        first end        -   which has a smaller outside diameter than an adjacent main            portion            -   whose external surface is, at least in part, a first                surface to be brazed;    -   the second component is a cylindrical steel sleeve        -   whose inside diameter is equal to the outside diameter of            the main portion of the first component and        -   whose internal surface is, at least in part, a second            surface to be brazed;    -   a silver-copper-palladium brazing alloy is placed around the        first end of the first component;    -   the steel sleeve is slipped over the main portion of the        first-component; and    -   the first and second components and the silver-copper-palladium        brazing alloy are heated in a vacuum or an inert gas until the        silver-copper-palladium brazing alloy melts and wets the        surfaces to be brazed, and are then allowed to cool down;        -   whereby the compound arrangement is formed.

A first development of the second variant of the invention provides amethod wherein

-   -   the steel sleeve has an end projecting beyond the first end of        the first component of titanium;    -   the first component has a tapped blind hole at the first end;    -   a tube of stainless steel which has an outside diameter equal to        the inside diameter of the steel sleeve is provided at a first        end with an external thread fitting the thread of the tapped        blind hole; and    -   the projecting end of the steel sleeve is brazed to the tube.

A second development of the second variant of the invention, which canalso be used together with the first development, provides a methodwherein the main portion of the first component of titanium is providedwith a collar remote from the first end, said collar being covered byand serving as a stop for the steel sleeve.

A third development of the second variant of the invention, which canalso be used with the first development and/or the second development,provides a method wherein

-   -   the first component of titanium is provided with an axial bore        whose diameter is equal to the inside diameter of the tube of        stainless steel;    -   a titanium tube whose outside diameter is virtually equal to the        inside diameter of the tube is inserted into the tube and into        the axial bore; and    -   the titanium tube is electrically welded to the first component        in an inert-gas atmosphere.

In a preferred embodiment of the first or second variant of theinvention, which can also be used with the above developments, acomposition of 86.5 wt. % silver, 26.5 wt. % copper, and 5 wt. %palladium is used which is as free of residues as possible.

BRIEF DESCRIPTION of the DRAWINGS

The invention will now be explained in more detail with reference to theaccompanying drawings, in which embodiments are shown schematically inthe form of longitudinal sections, and in which like referencecharacters have been used to designate like parts. In a figure followinga figure in which a reference character appeared for the first time,this reference character is not shown again.

FIG. 1 shows a compound arrangement formed according to the secondvariant of the invention;

FIG. 2 shows a compound arrangement formed according to the above firstdevelopment;

FIG. 3 shows compound arrangement formed according to the above thirddevelopment;

FIG. 4 shows compound arrangement formed according to the above secondand third developments; and

FIG. 5 shows the use of the second variant of the invention in asingle-tube Coriolis mass flow sensor.

DETAILED DESCRIPTION of the INVENTION

FIG. 1 shows a compound arrangement 1 of a first component 11 oftitanium and a second component of stainless steel in a sectional view.According to the second variant of the invention, compound arrangement 1was formed by brazing with a silver-copper-palladiumbrazing alloy.

For this purpose, component 11 was provided with a cylindrical first end111 which has a smaller outside diameter than an adjoining main portion112. The external surface 113 of the latter is, at least in part, afirst surface to be brazed; in FIG. 1 this is the entire externalsurface 113. The main portion is followed, via a constriction 114, by anintegral flange 115.

At its end 111, component 11 is provided with a tapped blind hole 116which extends into main portion 112. From end 111, component 11 wasprovided with an axial bore 117; its function and the functions offlange 115 and tapped blind hole 116 are explained below.

The second component is a cylindrical steel sleeve 12 whose insidediameter is equal to the outside diameter of main portion 112 ofcomponent 11, and whose internal surface 123 is, at least in part, asecond surface to be brazed; in FIG. 1, this is the surface touchingexternal surface 113 of component 11.

A first end 121 of steel sleeve 12 terminates at the beginning ofconstriction 114, while a second end 122 projects beyond the end ofcomponent 11. This is by no means mandatory: Steel sleeve 12 may also beflush with or recede from end 111.

To form the compound arrangement, steel sleeve 12 is slipped over mainportion 112 of component 11, i.e., the outside diameter of the mainportion is slightly less than the inside diameter of the steel sleeve,so that the latter can be easily slipped on. Thus, in this condition,steel sleeve 12 encloses component 11 without clasping it tightly forthe time being.

After steel sleeve 12 has been slipped on, a silver-copper-palladiumbrazing alloy 13 is placed around the first end 111 of component 11, asindicated by broken lines. The amount of brazing alloy 13 is chosen tobe sufficient for brazing the two surfaces 113, 123. Brazing alloy 13may take the form of a prefabricated silver-copper-palladium wire, acorresponding ribbon, or a corresponding paste.

A silver-copper-palladium brazing alloy which has proved especiallysuitable is a composition of 68.5 wt. % silver, 26.5 wt. % copper, and 5wt. % palladium which is as free of residues as possible.

The arrangement consisting of component 11, steel sleeve 12, andsilver-copper-palladium brazing alloy 13 is then heated in a vacuum oran inert gas, since titanium oxidizes quickly when heated, until thebrazing alloy melts and penetrates into the gap between the surfaces tobe brazed and wets these surfaces as completely as possible. Then thearrangement is allowed to cool down, so that steel sleeve 12 claspscomponent 11 tightly. The formation of compound arrangement 11 is thuscompleted.

FIG. 2 shows a sectional view of a compound arrangement 1′ formedaccording to a development of the method explained with reference toFIG. 1. A tube 14 of stainless steel which was provided at a first end141 with an external thread 142 fitting the thread 116 of the tappedblind hole was screwed into the blind hole. Tube 14 has an outsidediameter equal to the inside diameter of steel sleeve 12. The projectingend 122 of steel sleeve 12 was welded to tube 14, as illustrated by aweld 143.

FIG. 3 shows a sectional view of a compound arrangement 1″ formedaccording to another development of the method explained with referenceto FIGS. 1 and 2. A titanium tube 15 whose outside diameter is virtuallyequal to the inside diameter of tube 13 was inserted into axial bore117. A first end 151 of titanium tube 15 was electrically welded at 153to component 11 in an inert-gas atmosphere.

FIG. 4 shows a cross-sectional view of a compound arrangement 1* formedaccording to still another development of the method explained withreference to FIGS. 1 to 3. Main portion 112 of component 11 of titaniumwas provided with a collar 118 remote from first end 111. Collar 118 iscovered by steel sleeve 12 and serves as a stop for the latter. To thisend, steel sleeve 12 was provided with a recess 128 which fits collar118.

FIG. 5 shows a cross-sectional view of a single-tube Coriolis mass flowsensor 10 in which the second variant of the invention, shown in FIGS. 1to 4, was used to advantage twice. Tube 14 of compound arrangement 1*expands into a funnel-like end portion 144 having a greater diameterthan tube 14.

A compound arrangement 1# which is symmetrical with respect to compoundarrangement 1* has a funnel-like end portion 144′. End portions 144,144′ are permanently connected with one another by a support tube 16,for example by being welded to the support tube all around. For thispurpose, end portions 144, 144′ are so designed that support tube 16 canbe slip-fitted to them and that the external surfaces of end portions144, 144′ are flush with the external surface of support tube 16.

The diameter of end portion 144, which is greater than the diameter oftube 14, is chosen so that the resulting hollow space can serve to mountan exciter assembly and sensors etc. on titantium tube 15. These, as iswell known, are necessary for a Coriolis mass flow sensor but have beenomitted in FIG. 5 for clarity.

By using the invention with a single-tube Coriolis massflow sensor,which, as is usual and as shown in FIG. 5, is provided with titaniumtube 15 as a vibrating measuring tube, very good joints can be producedbetween support tube 16 of stainless steel and flange 115 of titaniumand between titanium tube 15 and flange 115.

These joints between titanium and titanium and between titantium andsteel are necessary since both the junction between titanium tube 15 and(titanium) flange 115 and the junction between steel tube 14 and(titanium) flange 115 must remain tight under all operating conditions,particularly in case of changes in temperature. This is guaranteed,since the maximum permissible operating temperature of Coriolis massflow sensor 10 is far below the temperature of the above-explainedbrazing.

By means of flange 115 and the corresponding flange 115′ at compoundarrangement 1#, the single-tube Coriolis massflow sensor 10 can beinstalled in a pipe conducting the fluid to be measured fluid-tight.

The invention can be used to particular advantage in a single-tubeCoriolis mass flow sensor with a cantilever mass as is described in theprior U.S. Provisional Applications Ser. No. 60/032,906 filed Dec. 16,1996, and Ser. No. 60/036,192 filed Jan. 21, 1997 as well as thecorresponding U.S. Non-Provisional application Ser. No. 08/940,644 filedSep. 30, 1997 which are incorporated herein by reference.

1-20. (canceled)
 21. A compound arrangement comprising a first componentof metal being brazed to a second component of metal, said firstcomponent having a cylindrical external surface touching a cylindricalinternal surface of said second component, said first and said secondcomponents being parts of a Coriolis mass flow sensor including avibrating measuring tube for measuring a fluid conducted in a pipe,wherein the metal of said first component is titanium and the metal ofsaid second component is steel, wherein the first and second componentsare brazed with a brazing alloy comprising silver, copper and palladium,INSERT said brazing alloy selected from the group consisting of: a68Ag-27Cu-5Pd brazing alloy; a 58 Ag-32 Cu-10 Pd brazing alloy; a 65Ag-20 Cu-'5Pd brazing alloy; and a 54 Ag-21 Cu-25 Pd brazing alloy. 22.The compound arrangement as claimed in claim 21, wherein the firstcomponent is said vibrating measuring tube of said Coriolis mass flowsensor.
 23. The compound arrangement as claimed in claim 21, wherein thesecond component is a sleeve.
 24. The compound arrangement as claimed inclaim 21, wherein second component is a support tube of said Coriolismass flow sensor.
 25. The compound arrangement as claimed in claim 21,wherein the first component is a flange of said Coriolis mass flowsensor.
 26. The compound arrangement as claimed in claim 21, wherein thefirst component is a flange of said Coriolis mass flow sensor.
 27. Thecompound arrangement as claimed in claim 21, wherein the vibratingmeasuring tube is a straight tube.
 28. The compound arrangement asclaimed in claim 27, wherein the first component is a support tube ofsaid Coriolis mass flow sensor.
 29. The compound arrangement as claimedin claim 27, wherein the first component is a flange of said Coriolismass flow sensor.
 30. A Coriolis mass flow sensor comprising a titaniumcomponent and a steel component, which is joined with said titaniumcomponent by a brazing alloy, wherein the titanium component is avibrating measuring tube of said Coriolis mass flow sensor, and whereinthe brazing alloy comprises silver, copper and palladium, said brazingalloy selected from the group consisting of: 68 Ag-27 Cu-5 Pd brazingalloy: a 58 Ag-32 Cu-10 Pd brazing alloy: a 65 Ag-20 Cu-15 Pd brazingalloy, and a 54 Ag-21 Cu-25 Pd brazing alloy.
 31. A compound arrangementcomprising a first component of metal being brazed to a second componentof metal, said first component having an cylindrical external surfacetouching a cylindrical internal surface of said second component, saidfirst and said second components being parts of a Coriolis mass flowsensor including a vibrating measuring tube for measuring a fluidconducted in a pipe, wherein the metal of said first component istitanium and the metal of said second component is steel, and whereinthe first and second components are brazed with a brazing alloycomprising silver (Ag), copper (Cu) and palladium (Pd), said brazingalloy is a composition of 68.5 wt. % silver, 26.5 wt. % copper, and 5wt. % palladium.
 32. The compound arrangement as claimed in claim 31,wherein the first component is said vibrating measuring tube of saidCoriolis mass flow sensor.
 33. The compound arrangement as claimed inclaim 31, wherein the second component is a sleeve.
 34. The compoundarrangement as claimed in claim 31, wherein the second component is asupport tube of said Coriolis mass flow sensor.
 35. The compoundarrangement as claimed in claim 31, wherein the first component is aflange of said Coriolis mass flow sensor.
 36. The compound arrangementas claimed in claim 31, wherein the first component is a flange of saidCoriolis mass flow sensor and the second component is a support tube ofsaid Coriolis mass flow sensor.
 37. The compound arrangement as claimedin claim 31, wherein the vibrating measuring tube is a straight tube.38. The compound arrangement as claimed in claim 31, wherein the firstcomponent is a support tube of said Coriolis mass flow sensor.
 39. Thecompound arrangement as claimed in claim 31, wherein the first componentis a flange of said Coriolis mass flow sensor.
 40. A Coriolis mass flowsensor comprising a titanium component and a steel component, which isjoin with said titanium component by a brazing alloy, wherein thetitanium component is a vibrating measuring tube of said Coriolis massflow sensor, and wherein the brazing alloy comprises silver (Ag), copper(Cu) and palladium (Pd), said brazing is a composition of 68.5 wt. %silver, 26.5 wt. % copper, and 5 wt. % palladium.